UCC28070: PIN #14 GDA NO SIGNAL, PIN #17 GDB 10.2 SIGNAL

Eddie Loy

Part Number: UCC28070

I AM TESTING WITH NO LOAD AND/OR SWITCHES. I AM TESTING FOR OUTPUT SIGNAL BEFORE GOING FURTHER.

I AM USING A KNOWN WORKING UCC28070 IC THAT I BORROWED FROM A FRIEND WHO ACTUALLY SHOWED ME THAT IT WORKED IN HIS PFC CONTROLLER.

I PUT THAT SAME WORKING IC INTO MY BOARD AND GDA (Pin #14) WAS FLAT-LINE AT 200mV. BUT GDB (Pin #17) WAS WORKING FINE WITH A 10.6V OUTPUT SIGNAL WITH A SLIGHT DUTY CYCLE OSCILLATING BETWEEN 89% TO 96%.

Question 1) WHAT AREA OR PIN # SHOULD I BE CHECKING INTO THAT WOULD CAUSE GDA PIN #14 TO BE FLAT-LINED?

Question 2) EASE PROVIDE EXPLANATION WHY GDA HAS NO OUTPUT SIGNAL AND GDB HAS GOOD OUTPUT SIGNAL?

Question 3) DO YOU HAVE ANY LITERATURE, POST RELATING TO THIS SITUATION?

THANK YOU FOR YOUR SPEEDY RESPONSE.

over 6 years ago

0 John Griffin1 over 6 years ago

TI__Mastermind 34465 points

Hello Eddie Loy,

Obviously your board has some problem with the GDA output being overloaded.

I suggest you review your schematic or post the document if you require further help.

There is a comprehensive portfolio of reference designs, application notes, calculator tools and design tips at this web page

http://www.ti.com/sitesearch/docs/universalsearch.tsp?searchTerm=ucc28070#q=ucc28070&t=technicaldocument&linkId=3

Regards

0 Eddie Loy over 6 years ago in reply to John Griffin1

Intellectual 850 points

THANK YOU FOR YOUR RESPONSE.

I FOUND THAT I WAS BACK-FEEDING PIN #11 (GDA) WITH A 12VDC POWER. ONCE CORRECTED, I WAS ABLE TO SEE BOTH GDA AND GDB SIGNALS.

THIS BRINGS ME TO A PROBLEM WITH THE GDX SIGNALS.

I HAVE ATTACHED A LINK WITH THE GDX SIGNALS (PIC #1 THRU PIC #4). I DON'T KNOW HOW TO EXPLAIN WHAT THE SIGNALS ARE DOING. SO I ATTACHED PICS OF WHAT I AM SEEING ON THE SCOPE.

PLEASE REVIEW AND EXPLAIN WHAT THE SIGNALS ARE DOING AND WHICH PINS MIGHT BE AFFECTING THE GDX SIGNALS.

RIGHT NOW I HAVE NOTHING ATTACHED TO THE GDX OUTPUT PINS, SO I KNOW IT IS NOTHING DOWNSTREAM OF THE GDX PINS.

PLEASE REVIEW THE ATTACHED LINK OF THE GDX SIGNALS.

Question ) PLEASE PROVIDE DIRECTION ON WHAT IS CAUSING THIS AND IN WHAT AREA (PINS) THAT I SHOULD EXAMINE.

/cfs-file/__key/communityserver-discussions-components-files/196/FOUR-PICS-OF-GDX-SIGNALS-29-AUG-19--1258.pdf

THANK Y0U

EDDIE LOY

0 John Griffin1 over 6 years ago in reply to Eddie Loy

TI__Mastermind 34465 points

Hello EDDIE LOY,

I recommend that you perform the following:

(1) Replace the UCC28070 from your initial tests with a new part.
The previously used part was almost certainly damaged.

(2) Disable the dithering function of the UCC28070
This can be done by connecting the RDM pin to GND pin
and also
connecting the CDR pin to VREF pin

Regards

John

Power management

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UCC28070: PIN #14 GDA NO SIGNAL, PIN #17 GDB 10.2 SIGNAL